Re: concrete weight

[shawl@torchlake.com (Jonathan Shawl)]

Hi Gary, and all,
My point exactly! I was quoting Dave Irons on part of my last message.
I have not done the actual calculations yet, but I'm planning on it today.
I am thinking that any Psub should be under 8,000 lbs, because if you go over
that, you will have more expense in moving and launching. This would make it
unpractical as a Personal Sub. A friend of mine has a 14,000 Lb Steel Sub and he
had to get a special CDL drivers license so he could move it himself, not to
mention the tractor trailer rig needed. I know that at 4500 lbs, my sub is a
handful to transport and launch. So I will see what I can come up with for a
concrete sub hull in the 5-8 thousand lb range using the " hull thickness of . 08
the outside diameter of the hull." Does any one have the minimum safe thickness
for a concrete hull? I would not want to go any thinner than 3" on any concrete
hull, so I will use that as a minimum for now, unless someone has more info on
that. If this concrete sub idea won't float, I guess there would be no sense in
going into endless debate over the other aspects of concrete construction. Lets do
some Calcs and see how it comes out.
On my ribless, light Steel hull sub, the entire hull was about 1/3 the
displacement, 1/3 lead and iron ballast, and 1/3 in equipment and payload.
More later...
Jon Shawl

protek@shreve.net wrote:

> Jon,
>     Did you consider the end caps also in your "slightly buoyant"
> calculation?  Here is the problem; if you take a ratio of hull thickness to
> outside diameter that you feel you can live with and it only produces a
> "Slight" buoyancy then you have a major problem.  You have to fill this
> hull with hundreds or thousands of pounds of system components.  This
> requires the hull diameter to be gigantic.  Its a little like a business
> that buys an item for $1000 and sells it for $1010 with a ten dollar
> profit.  Can you imagine the volume you would have to move to make a living?
>     Jon, someone wrote me and said they were thinking about a concrete sub
> kit.  It would consist of a 3-foot diameter concrete pipe and two bird
> baths to be glued to the ends (glue is provided).
>     The foam you were talking about is called Syntactic Foam.  I am not
> sure of the spelling as usual, but it is "Very" expensive.  It does consist
> of glass beads in a resin matrix.  There are companies that sell the mix,
> to mix your own, or they will make your shapes for you by specs.  I have
> talked to them.  This foam is rated by depth in meters.  There is one other
> buoyancy solution similar to foam that I am not sure has been expressed on
> the site.  They make small "Spheres" that are 2 or 3 inches in diameter.
> These spheres can be used to fill a vacant flooded compartment or they can
> be glued together with epoxy to maintain a shape.  I think they are rated
> to 300 meters, but I am not sure about that figure.  I have thought of
> getting some to fill unused areas on my sub for extra payload carrying
> capacity.  If I introduce one more system to my sub I may have to loose
> weight one way or another.
>
> Gary Boucher
>
> At 01:42 AM 3/21/99 -0500, you wrote:
> >I think I found what I was looking for.
> >
> >Dave Irons said;
> >>"That would depend on the diameter of the hull
> >>A slightly buoyant submersible would could have a hull thickness of . 08 the
> >>outside diameter of the hull.  Example.  A five foot diameter hull = 4.8
> inch
> >>hull thickness.  A two meter diameter hull = 16 cm.  Most of the pressure
> >>hulls studied were slightly buoyant.  Most were thinner than . 08 so the
> numbers
> >are
> >>a little conservative."
> >
> >"slightly buoyant" Is good news for a underwater habitat because it won't
> take much
> >to hold it under water.
> >But I think a sub hull needs to be more than "slightly buoyant" or you
> will have to
> >add some other form of  non compressible buoyant material to help carry
> the payload
> >weight. This is the case with Alvin and some other "overweight" deep
> diving subs
> >that use a non compressible foam to add to their buoyancy. I think it is
> glass
> >micro bubbles in a resin. I'll bet that stuff is not cheep. Any body know
> about or
> >use this foam?
> >
> >Jon Shawl
> >
> >